1. Field of the Invention
The present disclosure relates generally to the manufacturing of a printed circuit board assembly, and more particularly, to a method that mounts an electronic component on a printed circuit board of an electronic device.
2. Description of the Related Art
When electronic devices operate, electronic components in the electronic devices emit electromagnetic waves. Since the emitted electromagnetic waves may create noise in the communication functions of the electronic devices, shield parts, i.e., shield unit mounting structures, for blocking the electromagnetic waves are often provided on upper surfaces of the electronic components, when the electronic components are mounted on substrates, such a printed circuit boards (PCBs).
The four general shield unit mounting structures include a mechanical shielding type, a clip type, a frame type, and a cover type.
In the mechanical shielding type, a shield unit is fastened to a substrate with screws, and a separate wall is welded to reinforce the surroundings of an important integrated circuit (IC) component. While the mechanical shielding type is easy to repair, it requires an additional process for screw fastening and has the weakest reliability, compared to other types of shield unit mounting structures.
The clip type includes a cover for shielding a component and clips for securing the cover to a substrate. Generally, the clips are mounted and bonded to the substrate along the periphery of the cover, and then the cover is fastened to the clips. The clip type is advantageous in terms of repair, space, and cost, but still requires a manual process for cover fastening and has a lower reliability than the frame type. Further, the cover is often separated from the clips.
The frame type includes a cover for shielding a component and a frame to which the cover is coupled. Because a single frame is used, the frame type has fewer components than the clip type, which uses a plurality of clips. In addition, because the area where the frame type structure is fixed to a substrate is larger than the clip type, the frame type has better reliability. However, due to the pick-up space and the width of the frame, the frame type has limitations in an under-fill applying process for a component bonded to the lower side of the frame and in a working space for repairing the component, and has a drawback that the height of the component increases.
The cover type includes only a cover, rather than a clip or a frame, and the cover itself is bonded to a substrate, similar to the mechanical shielding type. The cover type is advantageous in that the number of components is reduced to one and the total height of the component is low. However, after a shield unit is mounted, an under-fill resin cannot be applied to an IC component below the shield unit, and thus, the cover type cannot be applied to the mounting portion of a component requiring under-fill.
Components for performing various kinds of functions may be located below the various mounting forms of shield units described above. However, active elements consuming a large amount of power, such as an application processor (AP), a power amplifier module (PAM), a power management integrated circuit (PMIC), etc., generate a great deal of heat while operating. In order to prevent performance degradation due to this heat, a radiant-heat material, referred to as “thermal interface material (TIM)”, may be interposed between a heating component and a metal shield unit to rapidly transfer the heat generated from the component to the metal shield unit. In this case, a solid material in the form of a pad or sheet may be used as the TIM.
To mount the frame type of shield unit mounting structure, solder is printed on a substrate, an electronic component is then mounted, reflow soldering is added, an under-fill resin is applied, the under-fill resin is cured, and a shield unit cover to which a radiant-heat pad (e.g., a TIM pad) is attached is fastened.
Recently, a post-fastening process for a shield unit cover has been removed, and a shield unit frame and a cover that are integrally fastened to each other have often been mounted in order to enhance productivity.
However, because a radiant-heat material has to be brought close to a component and in order for the shield unit to achieve stable heat-transfer effect when the radiant-heat material is disposed below the shield unit, only the shield unit frame is mounted in the component mounting step, and thereafter, a shield unit cover to which a radiant-heat material is attached is manually fastened by applying pressure to a certain degree in the final process step.
Such a technology has a limitation in productivity enhancement, however, because the shield unit cover is manually fastened in the process. This is problematic in terms of product reliability because the compressive stress of the radiant-heat material between the component and the shield unit is transmitted to the whole substrate.